The present invention relates to a combinatorial weighing apparatus and, more particularly, to a combinatorial weighing apparatus of the type having a plurality of weighing hoppers and adapted for weighing materials through the steps of finding the weight of a batch of material in each weighing hopper, selecting the combination of weighing hoppers which gives a total weight equal to or closest to a preset target weight (referred to as the "best" combination, hereinunder) and discharging the batches of material from the weighing hoppers constituting the selected combination.
Generally, a combined weighing apparatus incorporating a computer, referred to as "computer scale", is used for accurately weighing materials which exhibit large variation in weight from one to another, e.g. fruits and vegetables, confectionaries, fabricated articles, perishables or the like.
In such a combinatorial weighing apparatus, batches of the material to be weighed are put into a plurality of weighing hoppers and weighed in respective hoppers. Then, the apparatus selects a combination of batches which provides a total weight closest to the target weight within a predetermined tolerance. The batches constituting the selected combination are then discharged and the evacuated weighing hoppers are charged with new batches of the material for the next cycle of the weighing operation. This operation is repeated to achieve the automatic weighing of the material.
Referring to prior art FIG. 1 schematically showing the mechanism of a combinatorial weighing apparatus, a distribution table 1 is adapted to disperse the material to be weighed in the radial direction and to distribute the dispersed batches of material to a plurality of weighing stations 2 arranged radially around the distribution table 1. The distribution table 1 is adapted to be vibrated by a vibrator or the like, so that the dispersed material is distributed to the weighing stations 2 as a result of the vibration of the table for a predetermined time length. In the illustrated embodiments, n weighing stations are arranged, and each weighing station 2 includes a distribution supply device 2a, pool hopper 2b, pool hopper gate 2c, weighing hopper 2d, weight sensor 2e, weighing hopper gate 2f and a hopper drive unit 2g. As shown in FIG. 2, the distribution supply device 2a is composed of a feeder base 2a-1 having a predetermined shape and a trough 2a-2 mounted on the feeder base 2a-1 through an electromagnet 2a-3 and a leaf spring 2a-4. As will be seen from FIGS. 3 and 4, a plurality of feeder bases 2a-1 are carried by a circular support member 3 through respective coiled springs 2a-5 and are arranged radially along the outer periphery of the distribution table 1. In operation, the material to be weighed is put on the distribution table 1 while the latter is vibrated reciprocatingly and spirally by an electromagnetic vibrator 4, so that the material is dispersed radially outwardly along the conical top surface of the distribution table 1 into separate batches which in turn are delivered to respective troughs 2a-9. The batch of material supplied to each trough 2a-2 is conveyed through the latter in the direction of the arrow as a result of a linear reciprocating vibration of the trough 2a-2 by the electromagnet 2a-3, and is put into the pool hopper 2b (FIG. 1) from the end of the trough 2a-2.
Referring back to FIG. 1, each pool hopper 2b is provided with a pool hopper gate 2c. As this pool hopper gate 2c is opened by the operation of the hopper drive unit 2g, the batch of material contained by the pool hopper 2b is put into the weighing hopper 2d. Each weighing hopper 2d is provided with a weight sensor 2e for weighing the batch of material put into the weighing hopper 2d. The output from the weight sensors 2e are delivered to a combination controlling section (not shown) which selects the best combination of the batches of material which provides a total weight most closely approximating the target weight within a predetermined tolerance. Each weighing hopper 2d is provided with a weighing hopper gate 2f. After the selection of the best combination, only the weighing hopper gates 2f of the weighing hoppers constituting the best combination are opened to let the batches of material go out of these hoppers. These batches of material are then collected at the lower central portion of the weighing apparatus through a collecting chute 5. The collecting chute 5 has a form resembling a conical funnel, and the batches of material dropping onto the peripheral portions of the chute are gathered at the central portion thereof naturally by the force of gravity or forcibly by a scraping means (not shown) or the like.
At the initial stage of the weighing operation, the weighing hoppers 2d are charged with respective batches of material to be weighed. The weight sensors 2e annexed to these weighing hoppers 2d weigh the batches of material and deliver weight signals L.sub.1 to L.sub.10 to the combination control section which is not shown. The combination control section then makes a computation of total weight for various hopper combinations and selects a combination which provides a total weight most closely approximating the target weight within a predetermined tolerance. The hopper drive unit 2g then opens the weighing hopper gates of the weighing hoppers constituting the selected best combination. In consequence, the batches of material providing the best combination are discharged from these hoppers 2d into the collecting chute 5. Then, the pool hopper gates 2c are opened to charge the evacuated weighing hoppers with new batches of material. At the same time, the distribution supply devices 2a corresponding to the evacuated pool hoppers 2b are vibrated for a predetermined time to charge the empty pool hoppers 2b with the material to be weighed. Then, the selection of the best combination is made in the same manner as that explained before. The weighing operation by the combinatorial weighing apparatus is thus performed repeatedly and continuously.
In the combinatorial weighing apparatus of the type mentioned above, it is essential that the supply and discharge of the materials to and from sections such as pool hoppers 2b, weighing hoppers 2d or the like have to be made independently without being interfered with by other sections. In the conventional combinatorial weighing apparatus, therefore, a plurality of drive units 2g are installed independently outside respective sections such as pool hoppers, weighing hoppers or the like, to ensure smooth supply and discharge of the material to and from respective sections.
According to this arrangement, however, the number of parts is increased impractically and the efficiency of use of power is lowered undesirably because a multiplicity of drive units 2g are arranged around respective sections such as pool hoppers 2b and weighing hoppers 2d. In addition, since the drive units 2g are arranged at the outer side of the pool hoppers 2b and the weighing hoppers 2d, the apparatus as a whole is projected radially outwardly requiring a larger installation space. The hoppers tend to be contaminated by deposition of the weighed material and, hence, have to be cleaned frequently. These hoppers, however, are not easy to access because of the presence of the hopper drive units 2g around these hoppers. Namely, troublesome work is required to demount the drive units at each time of the cleaning and this lowers the efficiency of the work.
The feeder base 2a-1 (See FIGS. 2 thru 4) can translate the vibration of the electromagnet 2a-3 effectively to the trough 2a-2 when its weight is large. It is, therefore, necessary to increase the weight of the feeder base 2a-1 as much as possible. In the distribution supply device 2a in the known combinatorial weighing apparatus, therefore, a weight 2a-6 is mounted so that the center of gravity is positioned at the rear part of the feeder base, i.e. at the end portion of the same close to the distribution table 1. The distribution supply devices 2a, each having the weights 2a-6, are arranged radially around the distribution table 1 independently of one another. The condition for the mounting of a multiplicity of distribution supply devices 2a around the distribution table 1 is that the weights 2a-6 of adjacent feeder bases do not interfere each other. For this reason, in the known combinatorial weighing apparatus, it is not possible to arrange a multiplicity of distribution devices 2a densely around the distribution table 1. Furthermore, since the distribution devices 2a are mounted on the support 3 (See FIG. 4) independently, the number of supporting members such as coiled springs is increased to raise the cost of the weighing apparatus as a whole.